Route planning devices are well known in the field of navigational instruments. The method of route planning implemented by known prior art systems depends on the capabilities of system resources, such as processor speed and the amount and speed of memory. As increased system capability also increases system cost, the method of route planning implemented by a navigation device is a function of overall system cost.
One feature of increased system capability involves off-route recalculation capabilities. Many conventional navigational devices simply do not incorporate an off-route recalculation functionality in order to reduce system complexity and maintain a low overall system cost. Some of these devices may alert the user that they are off course, but they do not perform any course recalculation. In these devices, the user must halt their journey or attempt to relocate themselves on the prior planned route via traditional navigation methods, e.g. asking directions or using a conventional map. With some devices, the user may still be able to see the previously planned route, but the user will have to employ his or her own decision making to chart back onto the displayed route. This can be time consuming and provide frustration to a user who is likely unfamiliar with the routes surrounding their errant location.
Additionally, in order to calculate a route it is necessary to select a starting position to begin the route calculation. The route calculation algorithm invariably takes a small but finite amount of time, maybe on the order of 10 to 20 seconds. If the current position of the device is used as the starting position for the route calculation, a new route is generated based on the position that was known historically. Thus, a moving device will have traveled some distance beyond that historical position. In other words, the new route will have a starting point which corresponds to the historical position which may or may not correspond to the device's current position. Thus, if a turn or other maneuver is indicated as a function of getting from the historical position (as known at the time the calculation was started) to a given destination, the device will easily be beyond the turn that was generated by the route calculation algorithm.
While stopping travel during the route calculation process may solve the stated problem of generating a route while in motion, in many cases halting travel is not a viable alternative. For example, when the user is traveling on an interstate it is entirely impossible to simply stop. The alternative of pulling off on the shoulder of a road is undesirable and can be dangerous. Pulling off on an exit is equally undesirable since doing so increases travel time and provides an added inconvenience to the user. In other instances, such as navigating downtown city streets, the traffic issues alone may prevent the user from stopping his or her vehicle during the recalculation process. Even if the user has the ability to safely stop his or her vehicle, such as when traveling in a neighborhood, the inconvenience factor is present.
In summary, current prior art systems have created a spectrum of products in which the degree of navigational accuracy is dictated primarily by the cost of the system. The lower cost systems currently offer a low degree of accuracy that is often inadequate for users. Therefore, there exists a need for a navigational route planning device which is more efficient and accurate than current low cost systems, without requiring more expensive system resources. In addition, there is also a need for a navigational route planning device which provides a user with more understandable, accurate and timely route calculation capabilities.